1. Field of the Invention
The present invention is directed to dermatological compositions. More particularly, the present invention is directed to urea compositions, methods of making urea compositions, and methods of using urea compositions to treat dermatological conditions.
2. Related Art
Urea is recognized as a cosmetic ingredient in formulations, typically acting as a humectant or a moisturizer. Urea is also recognized as a medically useful keratolytic agent because of urea's ability at high concentrations to solubilize and denature protein. For example, U.S. Pat. No. 5,919,470 describes dermatological compositions using concentrations of urea of about 21 to about 40 wt-% for treating xerosis and other skin conditions. Topical compositions of about 40 wt-% urea are available (for example, Carmol®40Rx, available from Doak Dermatologics, Fairfield, N.J.). Such compositions are useful for the treatment of various dermatological conditions, such as onychomycosis, as described in, for example, the following U.S. Pat. No. 6,281,239; U.S. Pat. No. 6,380,236; U.S. Pat. No. 6,429,231; and U.S. Pat. No. 6,673,842.
Such known compositions typically have a maximum concentration of urea of about 40 wt-%. This is because of the difficulty in dissolving or solubilizing all of the urea at concentrations above about 40 wt-%. At concentrations above about 40 wt-%, the urea cannot be fully dissolved in the aqueous medium or emulsion, resulting in precipitation of the excess urea. Precipitation becomes particularly acute when high concentrations of urea are dissolved at elevated temperatures (70-80° C.) at which the urea is more soluble, and then the mixture is cooled to room temperature range (20-25° C.). During the cooling process, the urea precipitates in the form of needles of urea (a crystalline phenomenon well known in chemistry), which result in a non-smooth gritty feel to the final product. Such a gritty feel resulting from concentrations of urea greater than 40% is exemplified by the Xerial 50 product, available from Laboratories SVR, Bondoufle, France (this product is labeled at 50% urea). Products having such a gritty feel are not ideal dermatological products—they are not absorbed into the skin quickly, and they can be painful when applied to any type of compromised skin.
There is thus a need in the art for methods of preparing urea compositions having a urea concentration above about 40 wt-% that are smooth and non-gritty. There is also a need in the art for such urea compositions. There is also a need in the art for urea compositions that incorporate other dermatologically useful components into a single composition. The present invention provides such methods and compositions.